convert-01.sql

CREATE TABLE conversion (
  from VARCHAR(50) NOT NULL ,
  to VARCHAR(50) NOT NULL ,
  conversion_factor DECIMAL (38, 10) NOT NULL
) ;

ALTER TABLE conversion 
  ADD CONSTRAINT pk_conversion
  PRIMARY KEY (from, to) ;

convert-02.sql

INSERT INTO conversion (from, to, conversion_factor) VALUES ('feet', 'meters', 0.3048);
INSERT INTO conversion (from, to, conversion_factor) VALUES ('meters', 'feet', 3.28084);

convert-03.sql

DECLARE @meters AS INT = 1.35;

SELECT @meters * conversion_factor AS feet
FROM   conversion
WHERE  from = 'meters'
       AND to = 'feet' ;